1. Field of the Invention
This invention relates in general to charging techniques for electronic devices and more particularly, to selectively controlling a power source for electronic devices.
2. Description of the Related Art
The use of portable devices, particularly mobile communications units, has exploded recently. Manufacturers are constantly adding features to these devices to make them more desirable to consumers. In addition, government agencies may order manufacturers to implement certain features in their devices. As an example, in part because of consumer demand and in part because of a government mandate, cellular telephone manufacturers have built Global Positioning System (GPS) receivers in their products. A GPS receiver can enable a cellular telephone to determine its physical location, which can be displayed to a user of the device or forwarded to some other entity, like an emergency operator.
GPS receivers typically include a reference oscillator circuit for purposes of synchronization. In particular, when a GPS receiver attempts to determine its location, the GPS receiver will establish communications with the appropriate satellites, relying on the reference oscillator circuit to do so. There is a possibility that the frequency of the reference oscillator circuit will drift, which may prolong the time that it takes for the GPS receiver to determine its location from the satellites. As an example, if the temperature of the reference oscillator circuit varies, the frequency of the reference oscillator circuit will vary, too. To help solve the problem of frequency drift, temperature-compensated oscillators (TCXO) have been developed, which can adjust the reference frequency in view of a temperature variation.
There are several ways in which the reference oscillator circuit may be subjected to heat. For example, almost all cellular telephones include charging circuits, which can be used to replenish rechargeable batteries. As the cellular telephone is charged, heat can be introduced into the device, which may cause frequency drift in the reference oscillator circuit of the GPS receiver. This variation in temperature even affects the performance of TCXOs.